1. DNA Structure and Function

2. Figure 16.1 How was the structure of DNA determined?

3. Overview: Life’s Operating Instructions
In 1953, James Watson and Francis Crick introduced an elegant double-helical model for the structure of deoxyribonucleic acid, or DNA
DNA, the substance of inheritance, is the most celebrated molecule of our time
Hereditary information is encoded in DNA and reproduced in all cells of the body
This DNA program directs the development of biochemical, anatomical, physiological, and (to some extent) behavioral traits

4. Building a Structural Model of DNA: Scientific Inquiry
After DNA was accepted as the genetic material, the challenge was to determine how its structure accounts for its role in heredity
Maurice Wilkins and Rosalind Franklin were using a technique called X-ray crystallography to study molecular structure
Franklin produced a picture of the DNA molecule using this technique

5. Franklin’s X-ray diffraction photograph of DNA
Figure 16.6 Rosalind Franklin and her X-ray diffraction photo of DNA.
(a) Rosalind Franklin
(b)
Franklin’s X-ray diffraction photograph of DNA

6. Franklin’s X-ray crystallographic images of DNA enabled Watson to deduce that DNA was helical
The X-ray images also enabled Watson to deduce the width of the helix and the spacing of the nitrogenous bases
The pattern in the photo suggested that the DNA molecule was made up of two strands, forming a double helix

7. 5 end 3 end 3 end 5 end Hydrogen bond 3.4 nm 1 nm 0.34 nm (a)
Figure 16.7
5 end C G
Hydrogen bond C G
3 end G C G C T A
3.4 nm T A G C G C C G A T
1 nm C G T A C G G C C G A T
Figure 16.7 The double helix. A T
3 end A T
0.34 nm
5 end T A
(a)
Key features of DNA structure
(b) Partial chemical structure
Space-filling model
(c)

9. Purine  purine: too wide
Pyrimidine  pyrimidine: too narrow
Figure 16.UN01 In-text figure, p. 310
Purine  pyrimidine: width consistent with X-ray data

10. Nucleotide Structure Each nucleotide consists of: phosphate group
Sugar group
ribose (RNA)
deoxyribose (DNA)
nitrogenous base
in this picture = adenine

11. Nucleotide Structure

12. Nitrogenous Bases Guanine (G) Adenine (A) Cytosine (C) Thymine (T)
Uracil (U)  replaces thymine in RNA

13. DNA Structure
Consists of a pair of nucleotide chains held together by hydrogen bonding between complimentary base pairs  creates double helical shape
A - T
C - G

14. Complementary Base Pairing
Nitrogenous bases united by hydrogen bonds
DNA base pairings
A-T and C-G
Law of complementary base pairing
one strand determines base sequence of other
Segment of DNA

15. DNA Replication DNA Helicase Complimentary base pairing DNA polymerase
Breaks hydrogen bonds between bases
Complimentary base pairing
DNA polymerase
Joins complimentary nucleotides forming new strand

16. The Basic Principle: Base Pairing to a Template Strand
Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication
In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules

17. (a) Parent molecule A T C G T A A T G C
Figure 16.9 A model for DNA replication: the basic concept.

18. (a) Parent molecule (b) Separation of strands A T A T C G C G T A T A
Figure 16.9 A model for DNA replication: the basic concept.

19. (a) Parent molecule (b) Separation of strands (c)G C G C G C G T A T A T A T A A T A T A T A T G C G C G C G C
(a) Parent molecule
(b)
Separation of strands
(c)
“Daughter” DNA molecules, each consisting of one parental strand and one new strand
Figure 16.9 A model for DNA replication: the basic concept.

21. Semiconservative Replication
One parental DNA strand is conserved and one newly synthesized strand is produced

22. Protein Synthesis

23. DNA Contains the instructions for protein synthesis
Sequence of bases codes for one protein
Specifically, a sequence of three bases codes for a particular amino acid (“triplet code”)

25. RNA: Structure and Function
Consists of a single chain of nucleotides
Ribose replaces deoxyribose as the sugar
Uracil replaces thymine as a nitrogenous base
Forms of RNA:
messenger RNA (mRNA)
transfer RNA (tRNA)
ribosomsal RNA (rRNA)
Function: interpret DNA code and direct protein synthesis in the cytosol (ribosome)

26. Genetic Code Method of information storage along DNA strands Codon:
Stored in the sequence of bases
Genetic code called “triplet code” because three base sequence codes for a single amino acid
Codon:
“mirror-image” sequence of bases found in mRNA
Complimentary base pairing

27. Preview of Protein Synthesis
Transcription
messenger RNA (mRNA) is formed next to an “activated” gene  copy of instructions is created
mRNA migrates to cytosol
Translation
mRNA code is “read” by ribosomal RNA as amino acids are assembled into a protein molecule
transfer RNA delivers the amino acids to the ribosome

28. Transcription Instructions are transcribed or copied from DNA to RNA
RNA polymerase binds to DNA
opens DNA helix and transcribes bases
Bases pair in complimentary manner
mRNA moves through nuclear envelope into cytosol and binds to ribosome

29. Translation of mRNA
Formation of linear chain of amino acids by using instructions mRNA
Codon on mRNA designates a particular amino acid

30. Transfer RNA (tRNA)
Binds specific amino acid and brings to ribosome to join amino acid to growing protein molecule
Anticodon binds to complementary codon on mRNA

31. DNA and Peptide Formation